The subject disclosure relates to an electric tool and, more particularly, to an electric tool having a function of an electric screw driver.
An electric screw driver, as a commonly-used household tool, has advantages such as portability, convenience, inexpensiveness, practical use and adaption for broad user groups. However, a non-professional or do-it-yourself (“DIY”) user, particularly, a housewife, the elderly and so on may have difficulty in controlling a screw advance depth, a bolt pre-tensioned torsion or the like so that usually such user's work fails or proves imperfect.
In the prior art, partial screw drivers have a mechanical torsion cup which is provided with a plurality of gearshifts adapted for different operation conditions respectively. However, since torsion values corresponding to the respective gearshifts are certain, the user cannot select a suitable gearshift completely according to their needs. If a corresponding gearshift cannot be selected, a close gearshift can only be selected. In this case, the user usually cannot duly control the machine to precisely complete the work, unless he has an excellent operation techniques and rich experiences.
In addition, even if the user selects a corresponding gearshift, it is usual that a screw is not screwed in place or screwed too tightly when the screw is screwed. In practice, the user usually desires to manually rotate the screw tight when the screw is about to be screwed tight, to ensure that the screw is screwed in place. However, such operation mode including electrical operation and manual operation is time-consuming and labor-consuming in the event of a large workload and therefore causes a lower working efficiency.